This proposal would capitalize on work with mammalian cells that indicates unscheduled DNA synthesis (U.D.S.) can occur as a result of exposure to agents that induce genetic lesions. Peripheral blood lymphocytes are essentially a non-dividing population and these cells present a unique opportunity to study repair capabilities (U.D.S.) in humans. In this investigation, optimum techniques to purify and prepare lymphocyte cultures will be developed. The ability, or lack of ability, of the cells to repair genetic lesions after exposure to compounds that are known to induce U.D.S. will be determined by suitable autoradiographic techniques. In the first year of this study, procedures to obtain a high yield of pure cultures will be developed, baseline studies on apparently normal individuals, age 20-30, will be undertaken and the variation of repair as determined by this procedure will be investigated as a function of age. In the second year of this project, repair capabilities in humans as a function of leukemia, malignancies other than leukemia and various disease states will be evaluated.